An organic electronic element is an element which performs an electrical operation by using an organic substance, and is expected to be able to exhibit features such as energy saving, low price, and flexibility. Thus, organic electronic elements are attracting public attention as a technology that replaces conventional inorganic semiconductors containing silicon as a main component.
Examples of the organic electronic element include organic EL elements, organic photoelectric conversion elements, and organic transistors.
Among the organic electronic elements, attention is being paid to organic EL elements for the application as a large-sized solid state light source, for example, as substitutes for incandescent lamps and gas filled lamps. Furthermore, attention is also paid to the organic EL elements as the most promising self-luminescent display devices that substitute liquid crystal displays (LCD) in the field of flat panel display (FPD), and thus productization of organic EL elements is underway.
In recent years, there has been attempt to use mixtures of charge transporting compounds and electron accepting compounds, for the purpose of improving the light emission efficiency and service life of organic EL elements.
For example, Patent Literature 1 discloses that an organic electroluminescent element capable of low voltage driving is obtained by mixing a hole transporting polymer compound with tris(4-bromophenylaminium hexachloroantimonate: TBPAH) as an electron accepting compound.
Furthermore, Patent Literature 2 discloses that a hole-transporting compound is used as a mixture with iron(III) chloride (FeCl3) as an electron accepting compound by a vacuum deposition method.
Patent Literature 3 discloses a hole transporting polymer compound is mixed with tris(pentafluorophenyl)borane (PPB) as an electron accepting compound by a wet film forming method, and the mixture is used to form a hole injection layer.
As such, it is contemplated that it is important to produce a compound formed from a radical cation of a charge transporting compound and a counter anion, which is produced by mixing a charge transporting compound with an electron-accepting compound.
Furthermore, Patent Literature 4 discloses a composition containing a particular aminium cation radical as a composition for charge-transporting film.
However, these literatures do not describe the purport of utilizing the ionic compounds related to the present invention as an electron-accepting compound.
On the other hand, organic EL elements are roughly classified into two classes of low molecular weight type organic EL elements and polymer type organic EL elements, based on the materials used and the film forming method. Polymer type organic EL elements are such that the organic materials are composed of polymeric materials, and the polymer type organic. EL elements are capable of simple film formation such as printing or inkjetting, as compared with low molecular weight type organic EL elements which require film formation in a vacuum system. Therefore, polymer type organic EL elements are elements that are indispensable for the large-screen organic EL display devices of the future.
Active research has been hitherto conducted in relation to low molecular weight organic EL elements as well as polymer type organic EL elements; however, low light emission efficiency and short element service life still remain as serious problems. As one measure to be taken to address these problems, low molecular weight type organic EL elements adopt multilayering.
FIG. 1 illustrates an example of a multilayered organic EL element. In FIG. 1, a layer that is in charge of light emission is designated as a light emitting layer 1, and when the organic EL element has other layers, a layer that is in contact with the positive electrode 2 is designated as a hole injection layer 3, while a layer that is in contact with the negative electrode 4 is designated as an electron injection layer 5. Furthermore, when another layer is present between the light emitting layer 1 and the hole injection layer 3, the layer is designated as a hole transport layer 6, and when another layer is present between the light emitting layer 1 and the electron injection layer 5, the layer is designated as an electron transport layer 7. Meanwhile, in FIG. 1, reference numeral 8 represents a substrate.
Since film formation is carried out by a vapor deposition method in a low molecular weight type organic EL element, multilayering can be easily achieved by performing vapor deposition while sequentially changing the compounds used. On the other hand, since film formation is carried out by using a wet process such as printing or inkjetting in a polymer type organic EL element, there is a problem that when an upper layer is applied, the lower layer is dissolved out. Therefore, multilayering in a polymer type organic EL element is difficult to achieve as compared in a low molecular weight organic EL element, and the effects of enhancing the light emission efficiency and improving the service life may not be obtained.
In order to cope with this problem, several methods have been hitherto proposed. One of them is a method of utilizing the difference in the solubility. For example, use can be made of an element having a two-layer structure composed of a hole injection layer formed from water-soluble polythiophene:polystyrenesulfonic acid (PEDOT:PSS), and a light emitting layer formed by using an aromatic organic solvent such as toluene. In this case, since the PEDOT:PSS layer is not dissolved in the aromatic solvent such as toluene, it is possible to produce a two-layer structure.
Furthermore, Non-Patent Literature 1 suggests an element having a three-layer structure utilizing compounds having greatly different solubilities.
Furthermore, Patent Literature 5 discloses an element having a three-layer structure in which a layer called interlayer layer is introduced on the PEDOT:PSS layer.
Also, in order to overcome such problems, Non-Patent Literatures 2 to 4 and Patent Literature 6 disclose methods of changing the solubility of compounds by utilizing a polymerization reaction of a siloxane compound, an oxetane group, a vinyl group or the like, and thereby insolubilizing the thin film in the solvent.
These methods for promoting multilayering are important; however, there are problems that when water-soluble PEDOT:PSS is used, it is necessary to remove any moisture remaining in the thin film, that when it is attempted to utilize the difference in solubility, there are limitations on the materials that can be used, or that the siloxane compound is unstable to moisture in air. Also there is a problem that the element characteristics are not satisfactory.
In order to utilize the polymerization reaction, it is necessary to add an appropriate polymerization initiator which undergoes reaction and degradation due to stimulation such as light or heat, and generates an acid, a base, a radical or the like.
Patent Literature 7, Patent Literature 8, and Patent Literature 9 disclose photoacid generators or initiators, each containing fluorine atoms.
However, these literatures lack descriptions on an organic electronic material which uses a photoacid generator or initiator containing fluorine atoms.